Chemistry of Life, The Journey of a Carbon Atom

As you enter the organelle a big protein tells you that to continue any further you need to form a chain with your fellow CHO molecules, eventually becoming a fatty acid, before the protein lets you go it say you have to choose between having a double carbon bond making you bend, or just have normal bond making you straight.

Image (https://dlc.dcccd.edu/images/biology/lesson3/saturated_and_unsaturated_fatty_acid_models.jpg)